Alzheimer's disease-like pathology-triggered oxidative stress, alterations in monoamines levels, and structural damage of locus coeruleus neurons are partially recovered by a mix of proteoglycans of embryonic genesis

Effects of β-amyloid (1-42) Administration on the Main Neurogenic Niches of the Adult Brain: Amyloid-Induced Neurodegeneration Influences Neurogenesis

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder and warrants further study as well as timely treatment. Additionally, the mechanisms of the brain's intrinsic defense against chronic injury are not yet fully understood. Herein, we examined the response of the main neurogenic niches to amyloid exposure and the associated changes in structure and synaptic activity. Flow cytometry of Nestin-, Vimentin-, Nestin/Vimentin-, NeuN-, GFAP-, NeuN/GFAP-, NSE-, BrdU-, Wnt-, BrdU/Wnt-, VEGF-, Sox14-, VEGF/Sox14-, Sox10-, Sox2-, Sox10/Sox2-, Bax-, and Bcl-xL-positive cells was performed in the subventricular zone (SVZ), hippocampus, and cerebral cortex of rat brains on 90th day after intracerebroventricular (i.c.v.) single injection of a fraction of β-amyloid (Aβ) (1-42). The relative structural changes in these areas and disruptions to synaptic activity in the entorhinal cortex-hippocampus circuit were also evaluated. Our flow analyses revealed a reduction in the numbers of Nestin-, Vimentin-, and Nestin/Vimentin-positive cells in neurogenic niches and the olfactory bulb. These changes were accompanied by an increased number of BrdU-positive cells in the hippocampus and SVZ. The latter changes were strongly correlated with changes in the numbers of VEGF- and VEGF/Sox14-positive cells. The morphological changes were characterized by significant neural loss, a characteristic shift in entorhinal cortex-hippocampus circuit activity, and decreased spontaneous alternation in a behavioral test. We conclude that although an injection of Aβ (1-42) induced stem cell proliferation and triggered neurogenesis at a certain stage, this process was incomplete and led to neural stem cell immaturity. We propose the idea of enhancing adult neurogenesis as a promising strategy for preventing dementia at healthy elderly people andpeople at high risk for developing AD, or treating patients diagnosed with AD.

Gossypetin- based therapeutics for cognitive dysfunction in chronic unpredictable stress- exposed mice

Chronic unpredictable stress (CUS) is a promising model for induction of cognition impairment. Stress induced memory dysfunction is linked to the activation of kynurenine (KYN) pathway. This pathway indicates that, chronic stress primarily promotes the release of excessive cortisol from the adrenal gland, which tends to activate microglia and further increases kynurenine and its downstream pathway, resulting in excessive quinolinic acid (QA), which further impairs brain derived neurotrophic factor (BDNF) levels and leads to neurodegeneration. Prior studies already established anti-oxidant and anti-depressant activity of gossypetin. This research study was mainly conducted to elaborate neuroprotective activity of gossypetin against CUS-induced cognition impairment via acting on kynurenine pathway. In this study, Swiss albino mice were exposed to various stressors for five weeks and then administered with gossypetin (5, 10 and 20 mg/kg, i.p.) from the 4^th to the 7^th week (from day 22 to 49). Several behavioral tests were carried out between days 36 to 49 (6^th and 7^th week) and further corticosterone, neurotransmitters, oxidative stress, and brain-derived neurotrophic factor (BDNF) levels were measured. Results state that CUS exposed mice showed significant improvement in the behavioral pattern after gossypetin treatment. Corticosterone levels and oxidative stress was also found to be significantly decreased in gossypetin (10 and 20 mg/kg, i.p.) treated mice when compared with CUS exposed mice. Whereas, serotonin, norepinephrine and BDNF levels were also found to be increased after gossypetin treatment. Hence, gossypetin can be considered as a neuroprotective agent against cognition impairment caused by chronic unpredictable stress.

Posttranscriptional regulation of Nrf2 through miRNAs and their role in Alzheimer's disease

The nuclear factor erythroid-derived 2-related factor 2 (NFE2L2/Nrf2) is a pivotal facilitator of cytoprotective responses against the oxidative/electrophilic insults. Upon activation, Nrf2 induces transcription of a wide range of cytoprotective genes having antioxidant response element (ARE) in their promoter region. Dysfunction in Nrf2 signaling has been linked to the pathogenesis of AD and several studies have suggested that boosting Nrf2 expression/activity by genetic or pharmacological approaches is beneficial in AD. Among the diverse mechanisms that regulate the Nrf2 signaling, miRNAs-mediated regulation of Nrf2 has gained much attention in recent years. Several miRNAs have been reported to directly repress the post-transcriptional expression of Nrf2 and thereby negatively regulate the Nrf2-dependent cellular cytoprotective response in AD. Moreover, several Nrf2 targeting miRNAs are misregulated in AD brains. This review is focused on the role of misregulated miRNAs that directly target Nrf2, in AD pathophysiology. Here, alongside a general description of functional interactions between miRNAs and Nrf2, we have reviewed the evidence indicating the possible role of these miRNAs in AD pathogenesis.

Neurodevelopmental Clues to Neurodegeneration

Neurodegenerative disorders are characterized by neuronal loss, usually in late life. But recently, abnormalities of proteins implicated in neurodegenerative disorders have been identified in disorders of childhood, raising the possibility that clues to susceptibility to and prevention of neurodegenerative disorders may be identifiable before symptoms of disease arise. This review leverages these new and evolving findings to test our hypothesis, first proposed in 2010, that proteins implicated in neurodegenerative disorders play important roles in brain development by examining evidence in the peer-reviewed literature published in the past five years for the relevance of these proteins in normal and disease-associated brain development.

Examining the Role of the Noradrenergic Locus Coeruleus for Predicting Attention and Brain Maintenance in Healthy Old Age and Disease: An MRI Structural Study for the Alzheimer's Disease Neuroimaging Initiative

The noradrenergic theory of Cognitive Reserve (Robertson, 2013-2014) postulates that the upregulation of the locus coeruleus-noradrenergic system (LC-NA) originating in the brainstem might facilitate cortical networks involved in attention, and protracted activation of this system throughout the lifespan may enhance cognitive stimulation contributing to reserve. To test the above-mentioned theory, a study was conducted on a sample of 686 participants (395 controls, 156 mild cognitive impairment, 135 Alzheimer's disease) investigating the relationship between LC volume, attentional performance and a biological index of brain maintenance (BrainPAD-an objective measure, which compares an individual's structural brain health, reflected by their voxel-wise grey matter density, to the state typically expected at that individual's age). Further analyses were carried out on reserve indices including education and occupational attainment. Volumetric variation across groups was also explored along with gender differences. Control analyses on the serotoninergic (5-HT), dopaminergic (DA) and cholinergic (Ach) systems were contrasted with the noradrenergic (NA) hypothesis. The antithetic relationships were also tested across the neuromodulatory subcortical systems. Results supported by Bayesian modelling showed that LC volume disproportionately predicted higher attentional performance as well as biological brain maintenance across the three groups. These findings lend support to the role of the noradrenergic system as a key mediator underpinning the neuropsychology of reserve, and they suggest that early prevention strategies focused on the noradrenergic system (e.g., cognitive-attentive training, physical exercise, pharmacological and dietary interventions) may yield important clinical benefits to mitigate cognitive impairment with age and disease.

The Involvement of Insulin-Like Growth Factor 1 and Nerve Growth Factor in Alzheimer's Disease-Like Pathology and Survival Role of the Mix of Embryonic Proteoglycans: Electrophysiological Fingerprint, Structural Changes and Regulatory Effects on Neurotrophins

Alzheimer’s disease (AD)-associated neurodegeneration is triggered by different fragments of amyloid beta (Aβ). Among them, Aβ (25–35) fragment plays a critical role in the development of neurodegeneration—it reduces synaptic integrity by disruption of excitatory/inhibitory ratio across networks and alters the growth factors synthesis. Thus, in this study, we aimed to identify the involvement of neurotrophic factors—the insulin-like growth factor 1 (IGF-1) and nerve growth factor (NGF)—of AD-like neurodegeneration induced by Aβ (25–35). Taking into account our previous findings on the neuroprotective effects of the mix of proteoglycans of embryonic genesis (PEG), it was suggested to test its regulatory effect on IGF-1 and NGF levels. To evaluate the progress of neurodegeneration, in vivo electrophysiological investigation of synaptic activity disruption of the entorhinal cortex–hippocampus circuit at AD was performed and the potential recovery effects of PEG with relative structural changes were provided. To reveal the direct effects of PEG on brain functional activity, the electrophysiological pattern of the single cells from nucleus supraopticus, sensomotor cortex and hippocampus after acute injection of PEG was examined. Our results demonstrated that after i.c.v. injection of Aβ (25–35), the level of NGF decreased in cerebral cortex and hypothalamus, and, in contrast, increased in hippocampus, prompting its multidirectional role in case of brain damage. The concentration of IGF-1 significantly increased in all investigated brain structures. The administration of PEG balanced the growth factor levels accompanied by substantial restoration of neural tissue architecture and synaptic activity. Acute injection of PEG activated the hypothalamic nucleus supraopticus and hippocampal neurons. IGF-1 and NGF levels were found to be elevated in animals receiving PEG in an absence of amyloid exposure. We suggest that IGF-1 and NGF play a critical role in the development of AD. At the same time, it becomes clear that the neuroprotective effects of PEG are likely mediated via the regulation of neurotrophins.

Alpha2-Adrenoblockers Regulate Development of Oxidative Stress and Cognitive Behaviour of Rats under Chronic Acoustic Stress Conditions

Noise is a wide-spread stress factor in modern life produced by urbanization, traffic, and an industrialized environment. Noise stress causes dysfunction and neurotransmission impairment in the central nervous system, as well as changes in hormone levels. In this study, we have examined the level of α-Tocopherol (α-T) and malondialdehyde (MDA) in plasma and the erythrocytes’ membrane (EM), as well as the behavioral characteristics of a noise-induced stress model in rats. In addition, the modulating effect of α²-adrenoblockers, beditin, and mesedin on the aforementioned parameters has been investigated. For these purposes, albino male rats were divided into four groups: (1) untreated; (2) noise-exposed, (3) noise-exposed and beditin-treated (2 mg/kg, i.p.), and (4) noise-exposed and mesedin-treated (10 mg/kg, i.p.) animals. Noise-exposed groups were treated with 91dBA noise on 60 days with a daily duration of 8 h. Increased MDA and decreased α-T levels in plasma and EM were observed upon chronic high-level noise exposure. Locomotor and behavioral activity assessed with a Y-maze revealed disorientation and increased anxiety under chronic noise exposure. Prominently, α²-adrenoblockers alleviated both behavioral deficits and oxidative stress, providing evidence for the involvement of α²-adrenoceptor in the pathophysiology of noise-induced stress.

Embryonic proteoglycans regulate monoamines in the rat frontal cortex and hippocampus in Alzheimer's disease-like pathology

Using the rat Alzheimer's disease (AD)-like model we have analyzed the hippocampal short-term potentiation, levels of monoamines, and morphological changes in the hippocampal and cortical neurons after the administration of proteoglycans of embryonic origin (PEG). Results showed that the levels of monoamines and especially norepinephrine in the target AD brain structures were found elevated, except serotonin, which was unaffected in the hippocampus, but decreased in the frontal cortex. These changes were accompanied by the substantial structural damage of cortical and hippocampal neurons. PEG was able to reverse most of these changes. In addition, PEG administration had regime-dependent effects on a short-term potentiation pattern of hippocampal neurons. The elevated levels of key elements of brain monoaminergic system in the model of AD support the hypothesis of the important role of monoamines in the excessive synaptic excitation resulting in cognitive dysfunction in AD brain. The neuroprotective effect of PEG, as manifested by the recovery of the monoaminergic system, suggests this bioactive substance as a perspective therapeutic agent for the treatment of AD.